1. Field of Invention
The present invention relates to a cooling device and a control circuit thereof. More particularly, the present invention relates to a device and a control circuit for cooling an integrated circuit (IC) in the application of a microprocessor in a computer system.
2. Description of Related Art
FIG. 1 is a circuit diagram showing a conventional cooling fan control circuit for cooling an integrated circuit. The integrated circuit 11 is connected to a voltage stabilizer 12 which supplies an operation voltage to the integrated circuit 11. The input terminal of the stabilizer 12 is connected to one terminal of a sense resistor 15 as well as the negative (−) input terminal of an operation amplifier 13. The other terminal of the sense resistor 15 is connected to a power source Vcc and the positive (+) terminal of the operation amplifier 13. The output terminal of the operation amplifier 13 is connected to a cooling fan 14. Using the above circuit connections, the current flowing through the sense resistor 15 will change according to the actual loading in the integrated circuit 11. That is, a higher current will pass through the sense resistor 15 when the loading in the integrated circuit 11 is increased. Since there is a voltage drop whenever a current flow through the sense resistor, the resulting voltage drop across the sense resistor 15 is fed into the input terminal of the operation amplifier 13 to be amplified. According to the amplified voltage drop of the loading, the spinning speed of the cooling fan can be determined as required to control the operation mode of the cooling fan.
With the system as shown in FIG. 1, while the computer system is turned off, the central processing unit (CPU, the integrated circuit) is still at a high temperature. After the computer is restarted, the cooling fan does not operate since the loading of the CPU is not large enough. The CPU is thus easily to burn out due to the high temperature.
Moreover, an output signal for the operation amplifier is continuously supplied to the cooling fan 14, thus, it causes an additional power consumption, especially in the application of notebook computer because a portable computer requires an additional battery to supply voltage to the CPU and the peripheries. The design of the conventional fan cooling apparatus will increase power consumption and reduce the lifetime of the battery. Furthermore, in case that the cooling fan is burned out, it can not be detected from the circuit design of the conventional system, and thus, the CPU easily burns out consequently.
As the portable electronic equipment has a great demand in smaller dimension and configuration, the heat dissipation design and function are very much restricted. For example, active heat dissipation devices for portable computers can only adapt those small and thin fans. Hence, the performance and efficiency of heat dissipation may be severely affected. To prevent possible mal-functioning or damages to the hardware caused by a poor heat dissipating effect, some portable computers are designed with a thermal sensor to detect internal temperature variation. As soon as the thermal sensor detects an abnormally high temperature, the system automatically lowers the system performance such as lowering the operating frequency and voltage, so that the system is under a state with a lower thermal energy and temperature. In contrast, when the system has a good heat dissipating (for example, when the system is in an air-conditioned room or in a ventilated environment), the detected temperature is within a normal operating range. The operation performance can be enhanced to a high efficiency operation mode with a high clock of an operating frequency. However, as the temperature variation reflects a result of heat dissipation mechanism, using the thermal sensor to switch the operation clock speed is inevitably slow responsive. Thus, when the system is over heated, the thermal sensor may not perform an appropriate execution speed and good performance in time.